1. Field of the Invention
The present invention relates to an optical component for a maskless exposure apparatus, and more particularly, to a micro-prism array or a micro-mirror array which is an optical component capable of screening diffused light such that the image of a pixel of a digital micro-mirror display (DMD) formed by a first image-forming lens in the maskless exposure apparatus gives no influence on the image of a neighboring pixel and of totally reflecting the light after reflection or diffraction at the same time, thus improving exposure performance by using the quantity of light being transmitted without a loss and increasing numerical apertures (NAs) at the same time.
2. Description of the Related Art
In general, the operation of passing light through a mask with a shape equal to or different from a circuit pattern to be made and transferring the shape from the mask to a photosensitizer using an optical system, i.e., the technique for forming a micro-pattern at a desired portion using a light source, is referred to as a photolithography process, and an apparatus for performing such a process is referred to as an exposure apparatus.
Such an exposure apparatus are frequently used in semiconductor industries, display industries, and the like. The exposure apparatus is divided into a proximity exposure apparatus and a projection exposure apparatus according to an exposure method. The projection exposure apparatus is divided into a large-area exposure apparatus (conventional exposure method) using a mask as illustrated in FIG. 12 and a maskless exposure apparatus (recently developed exposure method) using no mask as illustrated in FIG. 13.
The maskless exposure apparatus is an exposure method for reducing the image of a digital micro-mirror display (DMD) pixel with 13.8 μm down to 2 μm by using a DMD module with a pixel size of about 13.8 and a size of about 20 mm, a first image-forming lens called as a beam expander, a micro-lens array and an exposure lens called as an equimultiple second image-forming lens.
While the conventional large-area exposure apparatus using a mask is an apparatus for irradiating light onto a mask (reticle) from the back of the mask and performing large-area exposure by using one projection lens, the maskless exposure apparatus using a DMD rather than a mask is a recently developed exposure method. Since the area to be exposed is small, the maskless exposure apparatus selects a method for arranging several exposure optical systems (three exposure optical systems in FIG. 13) in parallel to expand the exposure area. In a case where the size of a pattern is relatively large, one projection lens is used as the exposure optical system. However, in a case where a micro-pattern is exposed, two projection lenses are used as the exposure optical systems, and a micro-lens array is interposed between the two projection lenses.
An example of the exposure apparatus using a maskless exposure method will be described. As illustrated in FIGS. 1, 2 and 3, the exposure apparatus includes a light source 10 for outputting (emitting) light Le; a light intensity distribution correcting optical system 20 for allowing the light Le outputted from the light source 10 to be incident thereto and correctly outputting the light Le so as to have approximately uniform light intensity distribution; a mirror for reflecting the light Le outputted from the light intensity distribution correcting optical system 20 to bend the direction of a light path; a digital micro-mirror display (DMD) 40 having a TIR prism 50 for totally reflecting the light Le reflected by the mirror 30 and transmitting the totally reflected light Le to the DMD 40 and micro-mirrors 41 that are a plurality of pixel portions for respectively performing space light modulations in response to predetermined control signals; a first image-forming optical system 61 including lenses 61a and 61b for image-forming the light with respect to which the space image modulations are performed by the respective micro-mirrors 41; a micro-lens array 63 including a plurality of micro-lenses 63a arranged as optical components that are respectively disposed in the vicinity of the image-forming positions of the light Le image-formed by the first image-forming optical system 61 and individually pass the light Le therethrough; an aperture array 64 including a plurality of apertures; a second image-forming optical system 62 including lenses 62a and 62b for image-forming the light Le respectively passing through the micro-lenses 63a and the apertures 64a on a material 70 for printed circuit board; and the like.
However, in the conventional maskless exposure apparatus 100 performs expanded image forming with respect to the image of the DMD 40, which formed in the first image-forming optical system 61 so that the size of a pixel (micro-mirror) is 13 μm and the interval between pixels is 1 μm, on the micro-lens array 63. In a case where the performance of the first image-forming optical system 61 is perfect or the alignment of the first image-forming optical system 61 is perfect in manufacture, the shape of the expanded image is a shape illustrated in FIG. 3, in which the interval between pixels is perfectly shown. However, in an actual situation, light incident to each of the pixels is diffused or has a position error due to the resolution and distortion of lenses, the numerical difference of lenses, the alignment error of lenses, and the like, and therefore, has influence on a neighboring pixel. As a result, this has influence on the exposure performance on the exposure surface 70, and therefore, it is difficult to perfectly realize a desired shaped pattern.
Meanwhile, the first image-forming optical system 61 may perform expanded image forming such as 2 times, 2.5 times or 3 times, or may perform equimultiple image forming. In the invention, an optical system for performing equimultiple image forming will be described as an example.
That is, in a case where an equimultiple optical system is used as the first image-forming optical system, it is assumed that the size of the pixels is about 13.8 μm, the interval between the pixels is about 1 μm, and the size of the aperture array 64 is about 3 μm. Then, the entire light incident through the micro-lenses 63a is not effectively transmitted to the apertures 64a, and a portion of the light is transmitted to the apertures 64a. That is, since the micro-lenses 63a is generally formed in the shape of a convex lens, a portion of the light Le passing through the respective micro-lenses 63a is not perfectly concentrated and transmitted by refraction, diffusion, and the like, and loss of light quantity occurs. Therefore, the light Le is not effectively outputted to the aperture array 64 including the small-sized apertures 64a. 